The present application is directed to systems and methods for rotating a rod string from the surface at substantially high speeds. It is also directed to rotating a rod string from the surface at substantially high speeds to drive a downhole pump.
One of skill in the art appreciates that pumps are used to extract fluids, such as crude oil or water, from a producing well. Often times this extraction process requires artificial lift, which can be carried out using a variety of known pumps, including but not limited to pump jacks, hydraulic pumping systems, progressing cavity pumps (PCPs), or electric submersible pumps (ESPs).
PCPs transfer target fluids to the surface via rotation of a helical rotor against a stationary metal/rubber stator. Rotation of the rotor causes fix sized fluid containing cavities to move, thereby displacing the fluid to the surface. The rotor is driven by a rod string rotated by a surface rotary drive.
A major advantage of the PCP design is that its motor components are positioned on the surface and safe from downhole well conditions. But PCPs also have significant drawbacks. In deep wells, they are driven from the surface through an often substantially long rod string. It is difficult to safely rotate a long rod string at high speeds. The higher the rotation speed, the easier it is to lose rod string stability and create dangerous rod string whip. Thus, most PCPs are driven from the surface at speeds below 500 rpms. In addition, downhole PCP components such as the elastomer and elastomer/metal bond can degrade in certain well conditions (e.g, light oils, hot temperatures, etc.).
The pump component of an ESP is a multistage centrifugal pump. The pump is driven by a sealed motor positioned downhole below the pump. The downhole motor is connected to a variable speed controller at the surface via an electrical cable. The motor rotates the ESPs impellers at substantially high speeds creating a centrifugal force that pushes the target fluids upwards to the surface.
Like PCPs, ESPs also have drawbacks. Many of the sub-surface components, including the motor, cable, and seals, are submerged in the well. Thus, these components are directly exposed to the well's hostile conditions. This exposure shortens the life of and often damages or ruins the components, requiring expensive and time consuming replacements.
There is currently no practical solution for safely rotating a rod string at high speeds to improve a surface-driven rod system's production rate. There are also only limited solutions for maintaining the integrity of ESP components in a well. But both surface-driven rod systems and ESPs provide significant advantages. Thus, there is need in the art for systems and methods that improve upon the advantages of these systems, but at the same time eliminate their disadvantages. In other words, there is need in the art for systems and methods that are designed to move sensitive and expensive equipment from downhole to the surface where they are safe from exposure to harsh well conditions.